The rapid increase in the incidence of gram-positive infections—including those caused by antibiotic-resistant bacteria—has sparked renewed interest in the development of novel classes of antibiotics. One such class is the lipopeptide antibiotics, which includes daptomycin. Daptomycin has potent bactericidal activity in vitro against clinically relevant gram-positive bacteria that cause serious and life-threatening diseases. These bacteria include, but are not limited to, resistant pathogens, such as vancomycin-resistant Enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), glycopeptide intermediary susceptible Staphylococcus aureus (GISA), coagulase-negative staphylococci (CNS), and penicillin-resistant Streptococcus pneumoniae (PRSP), for which there are very few therapeutic alternatives. See, e.g., Tally et al., 1999, Exp. Opin. Invest. Drugs 8:1223-1238. Daptomycin's inhibitory effect is a rapid, concentration-dependent bactericidal effect in vitro and in vivo, and a relatively prolonged concentration-dependent post-antibiotic effect in vivo.
Daptomycin is described by Baltz in Biotechnology of Antibiotics, 2nd Ed., ed. W. R. Strohl (New York: Marcel Dekker, Inc.), 1997, pp. 415-435. Daptomycin, also known as LY 146032, is a cyclic lipopeptide antibiotic that can be derived from the fermentation of Streptomyces roseosporus. Daptomycin is a member of the factor A-21978C0 type antibiotics of S. roseosporus and is comprised of a decanoyl side chain linked to the N-terminal tryptophan of a cyclic 13-amino acid peptide (FIG. 1). Daptomycin has an excellent profile of activity because it is highly effective against most gram-positive bacteria; it is highly bactericidal and fast-acting; it has a low resistance rate and is effective against antibiotic-resistant organisms. The compound is currently being developed in a variety of formulations to treat serious infections caused by bacteria, including, but not limited to, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE).
A number of U.S. patents describe A-21978C0 antibiotics and daptomycin-related lipopeptides including daptomycin (LY 146032). These patents also describe methods of producing and isolating the A-21978C0 antibiotics and daptomycin-related lipopeptides.
U.S. Pat. RE32,333, RE32,455, 4,800,157, 4,874,843, and 4,885,243 describe methods of synthesizing and isolating daptomycin from fermentation cultures of Streptomyces roseosporus. U.S. Pat. RE32,310, RE32,311, 4,537,717, 4,482,487 and 4,524,135 describe A-21978C0 antibiotics and methods of deacylating the A-21978C0 antibiotic and reacylating the peptide nucleus and antibiotic derivatives made by this process. U.S. Pat. No. 5,912,226 (hereafter the '226 patent) describes the identification and isolation of two impurities produced during the manufacture of daptomycin, anhydro-daptomycin and the β-isomer form of daptomycin. None of these U.S. patents discloses a method for precipitating or crystallizing a lipopeptide in a manner to increase purity of the lipopeptide.
U.S. Pat. No. 4,439,425 (hereafter the '425 patent) discloses a crystalline lipopeptide and a method of crystallizing the lipopeptide. The lipopeptide disclosed in the '425 patent is structurally dissimilar from daptomycin and daptomycin-related lipopeptides. U.S. Pat. No. 5,336,756 (hereafter the '756 patent) also discloses a crystalline cyclic lipopeptide comprising a hexapeptide. The crystalline cyclic lipopeptide disclosed in the '756 patent is also structurally dissimilar from daptomycin and daptomycin-related lipopeptides. The '756 patent discloses that the lipopeptide, an echinocandin-type compound, can be obtained when aqueous n-propanol is employed as the crystallizing solvent. See, e.g., cols. 1-2 of the '756 patent. Neither the '425 patent nor the '756 patent disclose methods of crystallizing or precipitating daptomycin or a daptomycin-related lipopeptide, nor do they disclose methods of crystallizing or precipitating lipopeptides produced by Streptomyces. 
It would be advantageous to develop a method of crystallizing or precipitating daptomycin and daptomycin-related lipopeptides to provide an improved purification method for these lipopeptides. In addition, a crystalline or highly purified precipitated form of daptomycin or other daptomycin-related lipopeptide would be useful in formulating pharmaceutical compositions for treating bacterial infections. Further, a crystalline or highly purified precipitated form of daptomycin or daptomycin-related lipopeptide would be useful in a method to make a sterile product, particularly bulk sterile product. Thus, there is a need for methods to produce crystalline or precipitated daptomycin and daptomycin-related lipopeptides and the crystalline or precipitated forms of the lipopeptides produced thereby. However, there has been no simple and robust method that has been effective in crystallizing or precipitating daptomycin or a daptomycin-related lipopeptide that results in a lipopeptide that is more pure after crystallization or precipitation than before.